Saturable switch



April 1960 D. A. BUCK 2,933,618

SATURABLE SWITCH Original Filed March 31, 1953 S Sheets-Sheet 1 Fig. I

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ATTORNEYS United States SATURABLE SWITCH Dudley Allen Buck, North Wilmington, Mass., assignor to Research Corporation, New York,;N.Y., a corporation of New York Original application March 31, 1953, Serial No. 345,766-

Divide-d and this application March 15, 1957. Serial No. 646,436

6 Claims. 01. 307- 88) tion is a division of an application, Serial No. 345,766,

filed on March 31, 1953, as a joint application of Ken neth H. Olsen and myself, and now converted to a sole application of Olsen.

This switch has the property of certain mechanical relay systems which are particularly well adapted to decoding and which allow the use of a relatively small number of control leads to select among a large number of output terminals. However, because it has no moving mechanical parts the present invention is capable of much faster switching operation than that .which could be achieved by a mechanical system. While certain circuits involving the use of a relatively large number of crystal diodes also have the above property of allowing a small number of leads to select among many terminals, they are handicapped by the fact that the crystal diode cannot itself handle a large current and is a relatively delicate element; furthermore, its high impedance characteristics prevent the handling of short voltage pulses.

It is therefore an object of this invention to provide a simple and precise all-electric means for rapidlyswitching among a large number of terminals.

It is a further object of this invention to produce a switch combining the voltage conversion properties of a transformer with the switching advantages of a coordinate matrix whereby nA control leads are capable of selecting between A output terminals, where A is a chosen base number, preferably 2.

In furtherance of these and other objects, a principal feature of the present invention is the use of saturable ferroelectric transmissive elements connected in coordinate groupings in such a way that at any given time all of the elements except the one through which transmission is desired are biased to cut-off by one or more control inputs. 7 V

Figure 1 illustrates a typical saturable magnetic switching element.

Figure 2 illustrates the flux diagrams of such an element.

. Figure 3 illustrates a basic version of the switch.

Figure 4 illustrates a modified version of the switch in which one of the control leads also functions as an input-output lead.

Figure 5 illustrates a second modified version of the switch suitable for use as a single-digit binary adder.

Figure 6 illustrates a third modification of the switch in which the'number of elements is reduced.

Figure 7 shows a switch using areas of non-linear dielectric for the saturable elements. 1

Figures 8 and 8a show a printed capacitor suitable for use in the circuit of Figure 7.

Although the embodiments shown in Figs. 1 to 6 are the invention of Kenneth HaOlsen, they will first be described, since the principles applicable thereto are also applicable to my invention which is specifically shown in Figs. 7, 8 and 8a.

The principle of operation of the switch will appear from a brief consideration of a magnetic bar such as that shown in Figure 1 and having properties similar to those which are illustrated in Figure 2. In Figure l is shown a magnetic bar 3 capable of acting as a transformer core and carrying three sets of windings, numbered 1, 2, and 4. Winding 1 functions as a driving winding'and is shown as connected to a source of alternating current. Winding 2 functions as a control winding, the control being effected by a direct current flowing through this lead. Winding 4 functions in the same way as the secondary of any transformer to detect changes in the flux of the core and produce an output which depends on changes in that flux. This element shown in Figure 1 operates as a saturable transformer in that when no direct current is flowing through winding 2 the alternating current power from the source 1 is transferred with only small losses to the output 4, as in a conventional transformer. However, when a direct current is passing through the control winding 2 little or no power is transferred from the input to the output.

Although the general principles of operation of a core excited by both alternating and direct current are known, they will be briefly outlined here, in conjunction with Figure 2 showing at a a curve similar to a conventional magnetization curve, with flux plotted against current (i). The diagram is simplified in that it shows no hysteresis loop. If an alternating current is then passed through thepower winding 1 the direction and intensity of the input current will be shown by the sine wave b of Figure 2 and the flux as a function of time will be as shown at c. If, however, the switch to the control winding 2 is closed and a direct current is allowed to pass through the winding, the condition of the magnetic element will be about point 6, on the saturation part of the characteristic, and if a sine wave b is fed into the winding 1, the flux will vary only slightly, as shown at c'. As is illustrated in 2c the change in the flux with time is very small. Since there is little or no change in the flux there will be little or no voltage induced in the output winding 4 of Figure 1.

While the power source here has been referred to as an alternating current source and the operation has been described in terms of AC. power it is apparent that a pulse current in either direction will be transmitted by the element in its unbiased state as is represented by bc, while a voltage pulse, if applied to the element in its saturated state, will induce only a negligible amount of change in the flux and hence of output.

It will be seen that the operation of the switching element is that of a saturable transformer and while the operation has been described in terms of an equal number of windings on the input and output leads it is possible to make use of the impedance matching characteristics of a transformer to achieve any desired ratio in current or voltage between the input and output leads. Furthermore, it is possible to use any electrically transmissive element which has a saturating input-to-output characteristic like that shown in Figure 2.

One-embodiment of the invention consists of a switch made of a number of the above-described magnetic elements and controlled in the above manner through a coordinate switching arrangement which is described below for the binary case. The basic switching circuit is shown in Figure 3. It consists of eight (2 magnetic bars or transformer elements as shown and numbered 81 through 88. Each element has one separate set of windings numbered 10, 20, 30, 40, 59, 60, 70 or 80, depending on the element with which it is connected. All of the elements have in common a series of windings from a generator or driver 17 each consisting of one or more turns around each of the elements in series. Ignoring for a moment the control windings and considering the switch as consisting only of the cores 81--88, each with an individual winding (10, 20, 30, etc.) and having also the driving windings 9198 in common, it will be seen that if an alternating current is delivered by the driver 17 it will drive all of the cores simultaneously and an output could be detected in each of the separate output coils 10, 20, 30, etc.

In order to have this device function as a switch (or commutator), the invention selectively allows transmission through any individual magnetic element While at the same time preventing transmission through the remaining elements. This is done by a series of control windings each of which is capable of preventing transmission through those cores to which it leads. In Figure 3 these control windings are arranged in three stages denoted by the numbers 12, 34 and 56. At each stage there is a double-throw selector switch or the equivalent which is capable of choosing one of the two control leads and each of these control leads in turn is capable of biasing half of the number of elements involved in the switch.

Stage 12 selects between control leads 21 and 22. Control lead 22 biases elements 81 through 84, while control 21 biases elements 85 through 88. Stage 34 selects between controls 23 and 24. Control lead 24 biases elements 81, 82, 85 and 86, while control 23 biases elements 83, 8d, 87, and 88. Stage 56 switches between control leads 25 and 26. Lead 26 biases 81, 83, 85 and 87, While lead 25 biases 82, 84, 86 and 88.

To illustrate the operation of this control system, assume that transmission through element 88 is desired. It is necessary that no current flow through control leads 21, 23 and 25 in order to achieve this result and therefore stages 12, 34 and 56 are switched to leads 22, 24, and 26, respectively. An examination of all the elements other than element 88 will show that the above switching arrangement results in at least one biasing current controlling each of these elements. If 17 generates a driving signal, this signal will result in a change of state of flux of element 88 only and therefore only at terminal 80 will there be an output sensed. (Conversely, for the driver 17 a detector may be substituted, and it will sense as an output only the input at terminal 80.)

In a like manner there is a unique combination of switching positions for the selector switches at 1'2, 34 and 56 which will permit transmission of a signal through any one of the elements while at the same time preventing transmission through all of the others. For example, to permit transmission through element 81 all of the switches would be reversed and current would be allowed to'pass through control leads 21, 23 and 25. V

A more general examination of the theory of the binary controlling matrix will show that each stage reduces the number of possible channels for a signal to one-half of the number selected by the previous stage. For example, where transmission through element 81 is desired, stage 12 is switched to lead 21 and thus permits transmission through elements 81 through 84'at stage 34. The biasing current through lead 23 at the next stage blocks transmission through elements 83 and 84 and therefore permits transmission only through elements 81 and 82. At stage 56 as between elements 81 and 82 passinga biasing current through lead 25 results in transmission of a signal through element 81 only.

V This geometric arrangement which reduces the possible number of channels in half at each stage'is related to the tree type of circuit commonly used with mechanical relays or other similar devices. A fundamental difference, however, is the fact that tree circuits require at each stage a number of elements corresponding to the number of channels involved. In the above arrangement, how ever, only one element is necessary for each channel,

can switch between thirty-two channels.

. 4 each element having a unique grouping of a relatively small number of control windings.

A general way of expressing the performance of such a switch is to say that it enables nA control leads to select between A channels. It is apparent that the advantages of using such a device increase greatly where large numbers of channels are involved. For example five toggle switches selecting between ten control leads In the preferred form, as shown, binary coding is used (i.e. A=2).

Frequently the stages which have been illustrated as those controlled by the selector switches will in practice be controlled by bi-Stable circuits which permit current to be drawn by either one of two channels depending upon which stable state it is in. This control means is particularly useful when a switch of this type is used with high speed binary digital computing equipment.

.It should be noted that this device is a relatively etficient means of controlling power because only the selected core changes its state. Since there is little or no change in the flux of the unselected cores, there is a negligible power loss from hysteresis effects in the elements other than the one chosen. Furthermore, variation in the number of turns of the input and output windings may be used to obtain varying degrees of voltage or current change between input and output.

One of the most useful applications for this device, however, depends not upon its properties as a switch or commutator but rather on its properties as a decoding device. Any given switching combination of stages 12, 34 and 56 will select one of the eight output terminals. This characteristic is particularly useful with typewriters using punched tape where the tape may be punched either for lead 21 or 22 and at the same time for 23 or 24 and for 25 or 26. This sort of binary coding may be applied not only to typewriters where characters of the alphabet are chosen from a code master tape, but generally to any sort of coding. Used in this manner the switch replaces tree type arrangements of relays or similar devices, involves many fewer elements, and attains greater speed. In the computing field this application may be used to convert directly from binary to arithmetic numbers.

Thus, if switch 56 represents the 2 column of binary numbers, switch 34 the 2 column, and 12 the 2 column, and terminals 21, 23 and 25 represent zeros, and terminals 22, 24 and 26 represent ones, then each setting of the toggles represents one of the binary numbers from 000 to 111, and the output coil so selected represents its decimal equivalent from 0 to 7, coil 10 being 0, coil 20 being 1, etc. (It can readily be seen how the addition of another column of control coils would permit conversion of binary numbers from 0000 to 1111 to their decimal equivalents from 0 to 16.)

The switch has been discussed in the form shown in Figure 3 because it is believed that this arrangement most easily illustrates the theory of operation. However, a simplified form shown in Figure 4 is believed to be preferable for many purposes. It will be seen that Figure 4 is identical with Figure 3 except for the fact that the common source shown as 17 in Figure 3 has been eliminated and another source 18 is shown as leading direct to stage 12, whereby either the upper four coils or the lower four may be excited from the source 8, depending on the position of the switch 12. While the use of the biasing current is limited to stages 34 and 56 the theory of operation is the same as that already described in that each stage permits transmission through one-half the element and blocks transmission through the other half. However, in this case stage 12, the windings of which have taken over the input and output functions of the common source 17 in Figure 3, operates by simply not choosing those elements through which transmission is not desired.

Biasing of these elements is therefore not necessary.

To illustrate this mode of operating it will be recalled that in Figure 3 choice of lead 22 at stage 12 biased eles I 5 mer ts 81 through 84 and permitted transmission through elements 85 through 88; In Figure 4 the selection of this Same lead also prevents a signal being transmitted through elements 81 through 84 since in this position these elements have no winding connected to the source. Lead 22 permits transmission through elements 85 through 88 since in this position of stage 12 these are the only elemeiits which possessthe common power (or sensing) winding.

Figure 5 shows a further modification of the present invention so that it serves as a binary adder, for use in digital computers. In the addition of two binary numbers, the operation on each column of figures is the addition of the two digits in the column plus the carry-over from the previous column to produce a sum-digit and a carryover to the next column. 1 Thus, for example,

C r y tra p eced scolumn 1'1 1 l A 101 1 plusB 7 1,10

sum (A-l-B) l 0 0 0 1 Carry to next column (0) 0 1 e 1 1 0 In thethird column, the two digits are zero and one, the carryover is one and the result is a sum of zero and carry of one. On this basis (A+B+C=sum+carry), an addition table may be set up:

4 Input Output Sum Carry Figure shows the modification such that by setting the two digits up on two of the control coil switches and setting the carry from the preceding column into the third control coil switch, and further, by providing two sets of output coils, one for sum-digits and one for carrydigits, a binary single-digit adder can be made.

Eight cores are provided, 81, 82, 83, 84', 85, 86', 87', 88', one for each of the combinations in the table above. A driver 17' energizes all of the cores. Each core carries three control coils and two output coils. All of the control coils are connected to switch terminals 21, 22, 23:,24, 25 and 26, a pair of terminals for each of the switches 12', 34 and 56', in the same manner as in Figure 3. Each terminal in a pair corresponds to one of the binary digits 1 or 0, and each of the switches corresponds to one of the columns A, B'or C in the table above. It has been explained already in connection with Figure 3 how energizing one of each of the pairs biases all the cores to cut-off except one,

The output coils are connected to terminals so that the output terms of the table which are appropriate to the given A- B-?-C combination are selected. The coils are connected in series to a sumpair ofterminals S0 and S1 and a carry pair of terminals C0 and C1. Each terminal in the pair represents a binary digit 0 or 1. Thus, if the switches (or flip-flops) 12', 34 and 56 are set so that A=1 (21'), B=0 (24'), and C, the carry from the preceding stage, =1 (25'), then, all the cores except 83 are. biased to cut-01f. Then, outputs appear only at terminals S0 and C1, representing a sum Zero and carry one. The carry is carried by suitable connections to the switch corresponding to 56 in a later digit adder. Thus, a sequence of single-digit adders, as shown in Figure 5, can be made to add two binary numbers of any desired length.

V Figure 6 shows a further variant of the present invention in which the number of cores is reduced from 2 to x 6 2n. The embodiment of Figure6 also has an advantage in that each of the control currents goes through only one winding, thus reducing the inductance associated with the switching operation and resultingin greater speed, In this system, however, the selected output terminal is one across which zero output appears.

Figure 6 shows a switching arrangement using the six cores 281, 282, 283, 284, 285 and 286 as transmissive elements. (In order to facilitate an understanding of Figure 6, reference characters similar to those of Figure 3 have been used, but prefixed by 2; thus, 281 corresponds to 81.) A driver 217 activates primary 281 to'298 coils to introduce a cyclically varying in the cores.

Control coils are provided to apply to the cores the saturating M.M.F. obtained from the DC. source 257. The various combinations of control coils are'selected by the three switches 212, 234 and 256, each of which selects one terminal from the following pairs of terminals: 221 and 222; 223 and 224; 225 and 226. As indicated by the designation of each switch as 2 2 or 2, it can readily be seenthat each position of the three switches represents one of the binary numbers from 000 (0) to 11 1 (7).

A plurality of output coils are provided on each of the cores which are interconnected to eight output terminals 210, 220, 230, 240, 250, 260, 270 and 280. Each output corresponds to a number from 0 to 7. It will be seen that the output coils are arranged the way the control coils were in Figure 2. That is, each successivebank of coils divides the coils of the preceding bank into two pairs. Thus, the coils on cores 286 and 285 divide the eight outputs into halves of four outputs each, the coils on cores 284 and 283 divide the eight outputs into quarters of two outputseach, dividing by two each of the halves set by cores 286 and 285. Finally, the last division into eighths is made by the coils on cores 282 and 281.

Because of this arrangement, each position of the three controlswitches uniquely selects one of the output terminals at which none of the input from the driver 217 appears. Thus, for the control switch position shown (binary number no output appears at terminal 270 (octal number 6). The property of the core-coil configuration is that the presence of a saturating D.C. input prevents an output from appearing; however, a coil on a saturated core can still carry signals from a coil in series with it. Thus, switch 212 activates terminal 221, cutting oft core 286, but leaving core 285 unsaturated. Therefore, an output appears in all the coils on core 285 and that output voltage will appear at the output terminals connected to those cores, even if all the other cores were saturated. Therefore, none of terminals 218, 220, 230 or 240 can be the selected terminal at which no output appears.

Similarly switch 234 leaves core 283 active, which will cause outputs to appear at terminals 210, 220, 2-50 and 260. Switch 256 leaves core 282 active, and outputs appear at terminals 220, 240, 260 and 288. The only terminal at which no output appears is terminal 270, which corresponds to octal number 6, which, in turn, corresponds to binary number 110, represented by the switch positions. Such a switch might be used by connecting the outputs to relays in such a way that all the relays except the one selected are held open by the outputs which appear at all but the selected output terminal. Another important application of the invention is in the control of a binary storage system using magnetic elements, such a system as that described in the copending application of Forrester, Serial No. 225,714, filed May 11, 1951, now Patent 2,736,880 granted February 28, 1956. The present invention permits a substantial reduction in the number of vacuum tubes or crystal diodes used to control such a memory.

Figures 7, 8, and 8a show my invention in which the 'saturable elements are not magnetic cores, but non-linear of the first stage produces an output.

'7 magnetic arrangement shown in Figure 3. Figures 8 and 8a show a printed capacitor suitable for use in such a circuit. 1

A non-linear or ferroelectric condenser has a chargevoltage characteristic like the flux-current characteristic of the saturable magnetic core shown in Figure 2. That is, the slope of the characteristic is essentially constant over a small range near the origin where charge is proportional to voltage, but as the input voltage is increased the ratio of charge to voltage decreases. Thus, a capacitor can be made whose output in response to a given input is substantially reduced by the presence of a DC. saturating or biasing voltage. The principle of operation of the circuit of Figure 7 is therefore the same as that of Figure 3. Means are provided for applying a DC. saturating excitation to cut off successive halves of the number of output channels. The control inputs are activated by a series of two-position switches, so arranged that a given setting of the switches uniquely selects a single output to be unsaturated and therefore substantially larger than the other outputs.

The operation of the circuit can be seen from an inspection of the first stage 97 of the circuit. The sheet dielectric 100 is of a non-linear material, as described above. On one face of the sheet is the condenser plate 101 and on the other side of the sheet the two plates 103 and 105. Fig. 8 shows the first stage as made up of a single dielectric sheet, but it will be apparent that separate condensers can be used by simply breaking the dielectric and plates between the plates 103 and 105 and providing a suitable electric connection across thetwo halves of the plate 101. The input excitation corresponding to that from the driver 17 of Figure 3 is applied to the plate 101 and the output of the stage is taken from the plates 103 and 105. These plates are connected by suitable resistors through the switch 150 to avoltage source which supplies a DC. saturating voltage. The value of the voltage is selected so as to drive the condenser to a point of operation such as that shown at 6 in Figure 2. With the switch 150 in the position shown, the terminal 152 is connected to the source and biases to cut 011 the plate 105. The plate 103 is connected through the terminal 154 to ground. Thus, in this position, the output from the plate 103 is substantially larger than that from the plate 105. With the switch 150 in the opposite position, the output from plate 105 would be substantially larger than that of plate 103.

The second stage of the circuit makes use of the same dielectric sheet 100, and hence, the plates 103 and 105 are shown again in the stage 98. Each of these plates now acts like the input plate 101 and the plate 103 activates the output plates 107 and 109 and the input plate 105 activates the output plates 111 and 113. The switch 160 selects for cut off either the plates 107 and 111 or the plates 109 and 113. The third stage of the circuit 99 similarly selects one-half of the output resulting from the input plates 107, 109, 111 or 113. Consequently, one of the eight outputs is selected by any position of the three switches 150, 160 and 170. In the position shown, the switch 150 cuts off the plate 105 and only the plate 103 Likewise, the switch 160 cuts off plate 107 so that only plate 109 passes on the input signal to the third stage 99. The final switch 170 cuts off the plate 121, so that the selected output is that from the plate 119. The circuit of Figure 7 can be modified in the same ways as that of Figure 3 to produce a circuit like that shown in Figure 4 or a binary adder like that shown in Figure 5.

The capacitor circuit of Figure 7 lends itself to the convenient techniques of circuit printing. A single sheet of non-linear dielectric material, such as barium titanate, may be used and the various condenser plates printed in silver on the sheet, as shown in Figures 8 and 8a. A symbol indicates a vector going into the plate of the drawing and a symbol 6 indicates a vector coming out of the plane of the drawing. The input plate 101 reaches the full height of the obverse surface of the dielectric sheet 100. Facing it on the reverse side are the plates 103 and 105 which extend along the width of the sheet to face respectively the plates 107 and 109, and 1'11 and 113 on the obverse side of-the condenser. These four plates, in turn, are extended along the width of the sheet 100 to face on the reverse side the final output plates 115, 117, 119, 121, 123, 125, 127 and 129. Thus, if no D.C. saturating excitations were applied, the input signal applied to the plate 101 would pass in as shown by the vector 97 to the plates 103 and 105, and would continue out, as shown by the vector 98 to the plates 107, 109, 111 and 113, and would finally cross the dielectric sheet a third time to reach the output plates on the reverse side. In the circuit of Figure 7 and the printed capacitor of Figures 8 and 8a the elements which correspond to the saturable magnetic cores of Figure 3 are strips of dielectric widthwise along the sheet 100 of height equal to the height of the output plates 115, 117, etc. The structures corresponding to the control coils of Figure 3 are the connections through the switches 1-50, and which' apply to the plates 103,105, 107, 109, 111, 113, and the eight small output plates, saturating D.C. voltages.

It will therefore be understood that the invention is broad in scope, and is not to be construed as limited simply to the embodiments shown. The switches based on none-linear dielectric elements may be connected so as to make the embodiments of Figures 3, 4 and 5, and also other embodiments which may be useful in various applications. It should further be understood that, although the invention has been described in terms of a binary system, the control coils could be arranged in a ternary system, or in an arrangement based on any number A. A outputs would be selected by n switches with A terminals, each terminal being connected to a control coil which cuts off one transmissive element. In such a case, A transmissive elements would be required, except in the embodiment of Figure 6 where nA elements are sufficient to select one of A output terminals.

Having thus described my invention, I claim:

1. Apparatus for controlling the transmission of electrical energy in a plurality of channels comprising a plurality of series capacitors each having a dielectric with saturable ferroelectric properties, the capacitors being arranged in stages of increasing numbers of channels, saturating means for the capacitors, and means for controlling saturation of selected portions of each stage.

2. Apparatus for controlling the transmission of electrical energy in a plurality of channels comprising a plurality of capacitive elements, each having a dielectric with a single electrode on one side and a number of electrodes on the other side, connections to arrange said elements in stages, the dielectric of each element having saturable ferroelectric properties, means for applying an input voltage to the capacitive element of one stage, connections to cause application of an output voltage from the capacitive element of any stage to capacitive elements of a succeeding stage, and saturating means to apply a saturating voltage to selected electrodes.

3. Apparatus for controlling the transmission of electrical energy comprising afirst-stage capacitive element comprising a dielectric and a single input electrode-on one side of the dielectric and a pair of output electrodes on the other side of the dielectric, a second-stagecapacitor having two capacitive elements, each with a single input electrode and a pair of output electrodes on opposite sides of a dielectric, the dielectric of each capacitor having saturable ferroelectric properties, connections between the'output electrodes of the first-stage capacitor and the input electrodes of the second-stage capacitor, saturating means for the capacitive elements, and switching means for selecting the elements to be saturated.

4, Apparatus according to claim 3 in which the switch- 9 ing means is arranged to apply a saturating voltage to half of the capacitive elements of each stage.

5. Apparatus for controlling the transmission of electrical energy comprising a plurality of capacitors arranged in stages, each capacitor having a dielectric with saturable terroelectric properties, the capacitor of the first stage having a single input electrode and a number of output electrodes, the capacitor of each succeeding stage having an input electrode connected to an output electrode of its preceding stage and having a number of output electrodes for each input electrode, saturating means connected with each output electrode, and switching means for applying saturating voltages to selected electrodes.

6. Apparatus according to claim 5 in which there is a pair of output electrodes for each input electrode, and the switching means is arranged to apply a saturating voltage to one of each pair of output electrodes.

References Cited in the file of this patent UNITED STATES PATENTS 2,666,195 Bachelet et al. Jan. 12, 1954 

